Method and Device for Estimating a Current Wheel Circumference of at Least One Wheel Arranged on a Vehicle

ABSTRACT

The invention relates to a method for estimating a current wheel circumference of at least one wheel arranged on a vehicle, said method comprising: determining a reference speed of the vehicle at a point in time by means of a reference apparatus, detecting a wheel rotational speed of the at least one wheel at said point in time by means of a wheel rotational speed sensor, estimating a single wheel-circumference value based on the determined reference speed and the detected wheel rotational speed for said point in time by means of a calculation apparatus, storing at least the estimated single wheel-circumference value in a circular buffer for said point in time, estimating a current wheel circumference based on the single wheel-circumference values stored in the circular buffer by the calculation apparatus, outputting the estimated current wheel circumference as a wheel circumference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/510,408 filed on Jul. 12, 2019, which claims priority to GermanPatent Application No. DE 10 2018 211 804.3, filed on Jul. 16, 2018 withthe German Patent and Trademark Office. The contents of the aforesaidPatent Applications are incorporated herein for all purposes.

TECHNICAL FIELD

The invention relates to a method and a device for estimating a currentwheel circumference of at least one wheel arranged on a vehicle.

BACKGROUND

For safe operation of a vehicle, in particular a motor vehicle, it isessential for a driver and/or for assistance systems of the vehicle toknow a reliable value for a current speed of the vehicle. In thisregard, legal provisions may require the display or provision of a valuefor the speed that is never too low.

In general, the speed of the vehicle is determined from a wheelrotational speed detected at at least one wheel, which can usually alsobe referred to as a tire, and from an estimated wheel circumference. Thevalue used for the wheel circumference is calculated using a mean valueof the wheel circumferences of the tire types provided and/or permittedfor the relevant vehicle and said value is provided with an additionalmargin of safety. Said wheel circumference is static and always greaterthan the actual wheel circumference.

Furthermore, it is known to estimate a current wheel circumference inconsideration of a speed-induced expansion of the tires, for example byincreasing the value used for the wheel circumference depending on thespeed.

Since the actual tire size and actual wheel circumference are not known,these cannot be considered to a sufficient extent in the known methods.This may result in wheel circumferences that differ by a fewcentimeters, depending on the range of tires provided for a vehicle andthe respective tire tolerances, for example. This produces excessivedeviations during the calculation of the speed of the vehicle.

A method and an arrangement for determining an updated wheelcircumference of at least one wheel arranged on a vehicle is known fromDE 10 2006 058 567 A1, the at least one wheel being assigned at leastone wheel circumference in a control unit and the wheel speed beingdetermined by means of the control unit depending on the rotationalspeed of the at least one wheel and regardless of the assigned wheelcircumference. According to the method, a reference speed of the vehicleand/or wheel that is independent of the determined wheel speed isdetermined, the deviation between the at least one wheel speed and thereference speed is ascertained, and the updated wheel circumference ofthe at least one wheel is determined depending on said deviation.

SUMMARY

An object of the invention is to provide a method and a device forestimating a current wheel circumference of at least one wheel arrangedon a vehicle, it being possible to estimate the current wheelcircumference in an improved manner.

The object is solved by a method and a device according to theindependent claims. Various embodiments are discussed in the dependentclaims and the following description.

In one aspect, a method for estimating a current wheel circumference ofat least one wheel arranged on a vehicle is provided, said methodcomprising the following steps:

-   -   determining a reference speed of the vehicle at a point in time        by a reference apparatus,    -   detecting a wheel rotational speed of the at least one wheel at        said point in time by a wheel rotational speed sensor,    -   estimating a single wheel-circumference value based on the        determined reference speed and the detected wheel rotational        speed for said point in time by a calculation apparatus,    -   storing at least the estimated single wheel-circumference value        in a circular buffer for said point in time,    -   repeating the preceding steps for at least one other point in        time,    -   estimating a current wheel circumference based on the single        wheel-circumference values stored in the circular buffer by the        calculation apparatus and    -   outputting the estimated current wheel circumference as a wheel        circumference signal.

In another aspect, a device for estimating a current wheel circumferenceof at least one wheel arranged on a vehicle is provided, said devicecomprising an input apparatus, a calculation apparatus, a circularbuffer, and an output apparatus. The input apparatus is configured toreceive a determined reference speed of the vehicle from a referenceapparatus at at least one point in time and to receive a wheelrotational speed of the at least one wheel from a wheel rotational speedsensor at the at least one point in time. The calculation apparatus isconfigured to estimate a single wheel-circumference value based on thereceived reference speed and the received wheel rotational speed for theat least one point in time and to store at least the estimated singlewheel-circumference value in the circular buffer. The calculationapparatus is further configured to estimate a current wheelcircumference based on single wheel-circumference values stored in thecircular buffer for a plurality of points in time. The output apparatusis configured to output the estimated current wheel circumference as awheel circumference signal.

BRIEF DESCRIPTION OF THE DRAWINGS In The Figs.

FIG. 1 is a schematic representation of an embodiment of a device forestimating a current wheel circumference of one wheel arranged on avehicle;

FIG. 2 shows a characteristic curve for determining the qualitydepending on the age of one wheel-circumference value in the circularbuffer;

FIG. 3 shows a characteristic curve for determining the qualitydepending on the reference speed;

FIG. 4 shows a characteristic curve for determining a weightingdepending on an overall quality of the circular buffer;

FIG. 5 shows a schematic temporal progression of an estimated currentwheel circumference for the purpose of clarifying a method, inparticular with respect to a learning and unlearning behavior; and

FIG. 6 is a schematic signal flow diagram of an embodiment of a methodfor estimating a current wheel circumference of at least one wheelarranged on a vehicle.

DETAILED DESCRIPTION

In one aspect, a method for estimating a current wheel circumference ofat least one wheel arranged on a vehicle is provided, said methodcomprising the following steps:

-   -   (a) determining a reference speed of the vehicle at a point in        time by means of a reference apparatus,    -   (b) detecting a wheel rotational speed of the at least one wheel        at said point in time by means of a wheel rotational speed        sensor,    -   (c) estimating a single wheel-circumference value based on the        determined reference speed and the detected wheel rotational        speed for said point in time by means of a calculation        apparatus,    -   (d) storing at least the estimated single wheel-circumference        value in a circular buffer for said point in time,    -   (e) repeating steps (a) to (d) for at least one other point in        time, estimating a current wheel circumference based on the        single wheel-circumference values stored in the circular buffer        by means of the calculation apparatus and outputting the        estimated current wheel circumference as a wheel circumference        signal.

A basic concept of the present aspect is to estimate a singlewheel-circumference value for each of a plurality of points in time,i.e., a value for the wheel circumference of the at least one wheel at apoint in time. The relevant estimation may be carried out by means of acalculation apparatus based on the reference speed of the vehicledetermined and/or received for a particular point in time and on thewheel rotational speed detected and/or received for said particularpoint in time, in that the reference speed is divided by the wheelrotational speed. The reference speed refers to a speed which isdetermined independently of a wheel rotational speed, wheelcircumference and/or number of revolutions per unit time of the at leastone wheel.

A circular buffer is populated with values successively in this wayafter start of travel. New values may be added every second, forexample. If all storage locations of the circular buffer are occupied,the oldest values are discarded and replaced by current values. If, forexample, the circular buffer comprises 30 storage locations for thesingle wheel-circumference values and if a current singlewheel-circumference value is added every second, in total the circularbuffer will comprise values for a time period of 30 seconds. A currentwheel circumference is estimated based on said singlewheel-circumference values stored in the circular buffer by means of thecalculation apparatus and is subsequently output as a wheelcircumference signal. Said wheel circumference signal may be output inan analog and/or a digital manner, for example in the form of acorresponding data packet.

A current speed of the vehicle may be estimated based on the wheelcircumference signal. For this purpose, the current wheel circumferenceencoded in the wheel circumference signal may in some embodiments bemultiplied by a current wheel rotational speed. The result produces anestimation of the current speed of the vehicle.

The method according to the present aspect and the device as discussedin the following have the benefit that a current wheel circumference canbe estimated in an improved manner and in particular dynamic effects,which cause the wheel circumference to change, for example acceleration,an increased speed, progressive abrasion of the tire and/or expansion ofthe tire, can be better taken into consideration. The method and thedevice make it possible to provide an improved estimation of the speedusing the estimated current wheel circumference and the wheel rotationalspeed, which can also be calculated in accordance with the increasedrequirements of the European New Car Assessment Programme (Euro-NCAP).

The reference apparatus may for example be a global navigation satellitesystem (GNSS), for example NAVSTAR GPS (USA), GLONASS (Russia), Galileo(Europe), or Beidou (China). In order to determine the reference speed,an associated signal of the global navigation satellite system may bereceived and evaluated. The determined reference speed may then betransmitted to the input apparatus and/or calculation apparatus. In someembodiments the reference speed is calculated by means of the Dopplereffect.

Alternatively or additionally and in some embodiments, the referenceapparatus may be a laser system, a radar apparatus, and/or a camera,which are configured to determine and provide a current reference speedof the vehicle. A plurality of reference apparatuses may also be usedand the respectively determined reference speeds of said referenceapparatuses may be merged into one reference speed.

The wheel rotational speed may in some embodiments be detected by awheel rotational speed sensor and supplied to the input apparatus and/orcalculation apparatus as a wheel rotational speed signal. The wheelrotational speed may also be provided indirectly by and/or queried froma driving dynamics control system (e.g., electronic stability control,ESC) of the vehicle.

Furthermore, it is possible in some embodiments for the reference speedand wheel rotational speed associated with a particular singlewheel-circumference value to also be stored in the circular buffer, andnot merely the single wheel-circumference values.

In some embodiments, the current wheel circumference is estimated basedon a weighted mean value of the single wheel-circumference values storedin the circular buffer. In the simplest case, the weighting can be thesame for each of the single wheel-circumference values. However, it mayalso be possible that the weighting is different for each singlewheel-circumference value. For example, older single wheel-circumferencevalues may be given a lower weighting than more current singlewheel-circumference values.

In some embodiments, a validity of the reference speed and wheelrotational speed is checked in each case, the single wheel-circumferencevalue only being estimated and stored for a point in time if thereference speed and wheel rotational speed are valid for said point intime. The reference speed and wheel rotational speed are consideredvalid, for example, if a single wheel-circumference value estimatedtherefrom is within a predefined tolerance range. Said tolerance rangeis for example defined as follows: A maximum value is estimated based onthe wheel circumference of the largest tire provided and/or permittedfor the vehicle. A margin of tolerance of, for example, 1.5% is alsoadded to said estimation. The result constitutes the upper limit for therange in which an estimated single wheel-circumference value must lie.The lower limit of said range is correspondingly calculated on the basisof the wheel circumference of the smallest tire provided and/orpermitted, reduced by a margin of tolerance of, for example, 2.5%. Ifthe estimated single wheel-circumference value is within this range, thedata pair consisting of reference speed and wheel rotational speed isconsidered valid, otherwise the data pair is discarded.

The validity may also be determined in some embodiments based onadditional parameters of the reference speed and/or wheel rotationalspeed. These may for example include a resolution, delay, age, quality,or residual error probability of the corresponding measured value forthe reference speed and/or wheel rotational speed. In case of the wheelrotational speed, a currently measured degree of slippage, aninclination, lateral acceleration, longitudinal acceleration, a steeringangle, and/or controlled braking operations may also be considered incorresponding embodiments.

In some embodiments, the quality of the single wheel-circumferencevalues stored in the circular buffer is determined/ascertained. Saiddetermined quality of each of the single wheel-circumference values maythen be considered during weighting, for example.

In some embodiments, the quality is determined in each case depending onthe age of the single wheel-circumference values in the circular buffer.In particular and in some embodiments, the quality of a singlewheel-circumference value in the circular buffer may be reduced withincreasing age, such that the currently added single wheel-circumferencevalue is of greater quality.

In some embodiments, the quality is determined in each case depending onthe determined reference speed associated with the relevant singlewheel-circumference values. This way, the fact that a reference speedcan be determined in a particularly reliable manner in certain speedranges but less reliably in others can be taken into consideration. Forexample, it has been shown that a reference speed determined by means ofa GNSS, in the range of 20 km/h to 120 km/h can be determined in a morereliable manner than speeds above or below said range. The quality mayfor example be defined as a function of the speed in the form of acharacteristic curve.

The quality may also be determined depending on additional parameters insome embodiments. A parameter of this kind may for example be thequality of the reference speed and/or reference apparatus, for examplethe quality of the signal delivered by a GNSS. A change in speed, anacceleration and/or the duration of an acceleration phase at the pointin time in question may also influence the quality.

For example, the single wheel-circumference values may each be weightedby their quality during estimation of the current wheel circumference,it then being necessary to normalize the result.

In some embodiments, an overall quality of the circular buffer isdetermined, the current wheel circumference additionally being estimatedon the basis of the determined overall quality of the circular buffer.The overall quality is for example calculated based on a sum of theindividual qualities of the single wheel- circumference values in thecircular buffer. The sum may, e.g., be normalized by means of a maximumpossible quality by dividing the sum of qualities by the maximumpossible quality. The overall quality of the circular buffer is ameasure of how reliable an estimated current wheel circumference is.

In some embodiments, the current wheel circumference is estimated basedon a characteristic curve, the characteristic curve defining a weightingbetween a wheel circumference estimated on the basis of the singlewheel-circumference values stored in the circular buffer and a fallbackwheel circumference depending on the overall quality of the circularbuffer. This has the benefit that learning and unlearning of a wheelcircumference is made possible. For example, if there are referencespeeds for populating the circular buffer with singlewheel-circumference values, an improved wheel circumference can betaught proceeding from the fallback wheel circumference. If there are nolonger any reference speeds at a later point in time, for examplebecause the reference apparatus is no longer delivering any signal orthe signal is of insufficient quality, the wheel circumference is thengradually restored to the fallback wheel circumference, i.e., anestimated wheel circumference is unlearned gradually. As a result, evenin the event of the reference apparatus, such as a GNSS, failing, areliable value that complies with the required specifications at alltimes is selected for the wheel circumference.

The individual weightings can be defined for example by means of acoefficient characteristic curve that is dependent on the overallquality. The current wheel circumference can then be estimated asfollows:

Current wheel circumference=(coefficient from characteristic curve)*(wheel circumference estimated using single wheel-circumference values)+(1−coefficient from characteristic curve)*fallback wheel circumference

Over a course of the characteristic curve, a learning and unlearningbehavior of the method and/or device can be influenced during estimationof the current wheel circumference in some embodiments. For example, bymeans of the characteristic curve, the value for the estimated currentwheel circumference in the region of low overall quality of the circularbuffer can be set such that it can move away only very slowly from thefallback wheel circumference. However, in the region of greater overallquality of the circular buffer, the weighting can be selected such thatthe current wheel circumference estimated based on the stored singlewheel-circumference values can move away far more rapidly from thefallback wheel circumference.

The learning and unlearning behavior may also be made to depend on otheror additional variables. For example, the wheel circumference may beunlearned if a particular inclination is measured. Said unlearning mayalso take place during travel through a tunnel.

In some embodiments, the associated determined reference speed at arelevant point in time is additionally stored in the circular buffer,the current wheel circumference being estimated exclusively on the basisof the single wheel-circumference values in the circular buffer of whichthe associated reference speeds correspond to a speed range within whicha speed of the vehicle lies at a current point in time. As a result, thecurrent wheel circumference can be estimated in an improved manner,since said wheel circumference can be estimated specially for aparticular speed range.

It is also possible in some embodiments for the method to be carried outfor more than one wheel of the vehicle, i.e., at least one additionalwheel or even all wheels of the vehicle. The method then provides anassociated estimated current wheel circumference for each of the wheels.

The estimated current wheel circumference and/or wheel circumferencesignal may in some embodiments be limited with regard to a rate ofchange prior to being output and/or provided, for example limited to amaximum rate of change of 20 mm/s. As a result, an excessively fastchange of the estimated wheel circumference may be prevented.

In another aspect, a device for estimating a current wheel circumferenceof at least one wheel arranged on a vehicle is provided, said devicecomprising an input apparatus, a calculation apparatus, a circularbuffer, and an output apparatus. The input apparatus is configured toreceive a determined reference speed of the vehicle from a referenceapparatus at at least one point in time and to receive a wheelrotational speed of the at least one wheel from a wheel rotational speedsensor at the at least one point in time. The calculation apparatus isconfigured to estimate a single wheel-circumference value based on thereceived reference speed and the received wheel rotational speed for theat least one point in time and to store at least the estimated singlewheel-circumference value in the circular buffer. The calculationapparatus is further configured to estimate a current wheelcircumference based on single wheel-circumference values stored in thecircular buffer for a plurality of points in time. The output apparatusis configured to output the estimated current wheel circumference as awheel circumference signal.

The individual embodiments of the method, described in the preceding,may be implemented correspondingly in the device of the present aspect,the device in each case being configured to carry out the correspondingmethod or one or more method steps of the method. The benefits ofcorresponding embodiments of the device are the same as those ofcorresponding embodiments of the method.

In the following, the invention will be explained in greater detailbased on further exemplary embodiments and with reference to thedrawings.

FIG. 1 is a schematic representation of an embodiment of a device 1 forestimating a current wheel circumference 14 of one wheel 51 arranged ona vehicle 50. The device 1 comprises an input apparatus 2, a calculationapparatus 3, a circular buffer 4, and an output apparatus 5.

The input apparatus 2 receives a reference speed 10 of the vehicledetermined and provided by a reference apparatus 30. The referenceapparatus 30 may for example be a GNSS. Furthermore, the input apparatus2 receives a wheel rotational speed 11 of the wheel 51 of the vehicle.The wheel rotational speed 11 is detected by a wheel rotational speedsensor (not shown) and is provided as a corresponding signal for exampleby a driving dynamics control system 52 (ESC) of the vehicle 50. Theinput apparatus 2 synchronizes the reference speed 10 and the wheelrotational speed 11 in terms of their time base, such that data pairsconsisting of the reference speed 10 and the wheel rotational speed 11relate to the same point in time. The formed data pairs 12 are suppliedto the calculation apparatus 3.

The calculation apparatus 3 estimates a single wheel-circumference value13 for the data pair 12 based on the received reference speed 10 and thereceived wheel rotational speed 11 for the associated point in time (inFIG. 1 denoted by the index i). The estimated single wheel-circumferencevalue 13 is subsequently stored in the circular buffer 4 for said pointin time by the calculation apparatus 3.

This is carried out for additional data pairs 12 and/or additionalpoints in time and this way the circular buffer 4 is populated withestimated single wheel-circumference values 13. Current estimated singlewheel-circumference values 13 may for example be stored in the circularbuffer 4 every second. If the circular buffer 4 comprises 30 storagelocations, for example, values will therefore be stored successively forthe last 30 seconds in each case.

The calculation apparatus 3 estimates a current wheel circumference 14based on the single wheel-circumference values 13 stored in the circularbuffer 4 for the plurality of points in time.

The current wheel circumference 14 may be estimated based on a weightedmean value of the single wheel-circumference values 13 stored in thecircular buffer 4.

The output apparatus 5 subsequently outputs the estimated current wheelcircumference 14 as a wheel circumference signal 15. Said wheelcircumference signal 15 may be analog or digital, for example in theform of a corresponding data packet. A current speed 16 of the vehicle50, in particular, can be calculated based on the current wheelcircumference 14 and/or wheel circumference signal 15 by multiplying thecurrent wheel circumference 14 and/or wheel circumference signal 15 bythe wheel rotational speed 11, for example in a control system 53 of thevehicle 50.

A validity of the reference speed 10 and wheel rotational speed 11 canbe checked in each case, the single wheel-circumference value 13 onlybeing estimated and stored for a point in time if the reference speed 10and wheel rotational speed 11 are valid for said point in time. Thereference speed 10 and wheel rotational speed 11 are valid, for example,if the single wheel-circumference value 13 calculated therefrom lieswithin a predefined range.

The quality 17 of the single wheel-circumference values 13 stored in thecircular buffer 4 can be determined. Said quality 17 may for example bethe starting point for the selection of the weightings of the singlewheel-circumference values 13 during estimation of the current wheelcircumference 14.

The quality 17 may be determined in each case depending on the age ofthe single wheel-circumference values 13 in the circular buffer 4. Acharacteristic curve for ascertaining the quality 17 depending on theage is shown by way of example in FIG. 2. The age, i.e., temporalposition, of the relevant single wheel-circumference value 13 in thecircular buffer 4 is shown on the x-axis 20. As a maximum, the age canadopt a value that corresponds to a number n of storage locations in thecircular buffer 4. The y-axis 21 shows the quality 17, which is assignedto the corresponding age. The curve 22 formed shows that, in thisexample, the quality 17 decreases ever more strongly with age.

Alternatively or additionally, the quality 17 can be determined in eachcase depending on the determined reference speed 10 associated with therelevant single wheel-circumference values 13. A characteristic curvefor determining the quality 17 depending on the reference speed 10 isshown by way of example in FIG. 3. The reference speed 10 of the vehicle50 in km/h is shown on the x-axis 24. The y-axis 25 shows the quality17, which is assigned to the corresponding reference speed 10. The curve26 shown by way of example in FIG. 3 in particular takes into accountthe fact that the quality 17 decreases markedly below a speed of 20 km/hand above a speed of 160 km/h. This is the case for example with areference speed 10 provided by means of a GNSS.

If the quality 17 is ascertained depending on a plurality of parameters,the corresponding values are multiplied by one another.

An overall quality 18 of the circular buffer 4 can be determined by thecalculation apparatus 3, the current wheel circumference 14 additionallybeing estimated on the basis of the ascertained overall quality 18 ofthe circular buffer 4. For example, if a maximum quality 17 of eachsingle wheel-circumference value 13 is equal to 1 and if the circularbuffer 4 comprises 30 storage locations, for example, the overallquality 18 can adopt the value of 30 as a maximum without renewednormalization.

Furthermore, the current wheel circumference 14 can be estimated basedon a characteristic curve, the characteristic curve defining a weightingbetween a wheel circumference estimated on the basis of the singlewheel-circumference values 13 stored in the circular buffer 4 and afallback wheel circumference 19 depending on the overall quality 18 ofthe circular buffer 4. The fallback wheel circumference 19 is inparticular a legally prescribed value for the wheel circumference. Thevalue is calculated on the basis of a wheel circumference averaged fromthe tires provided for the vehicle 50, a margin of safety of, forexample, 4% also being added to the result.

A characteristic curve exemplifying this is shown in FIG. 4. The overallquality 18 ascertained for the circular buffer 4 at a current point intime is plotted on the x-axis 27. The y-axis 28 shows a weightingcoefficient which defines a weighting between the wheel circumferenceestimated on the basis of the single wheel-circumference values 13stored in the circular buffer 4 and a fallback wheel circumference 19.The larger the value of the weighting, the greater the extent to whichthe single wheel-circumference values 13 in the circular buffer aretaken into consideration; the smaller the value of the weighting, thegreater the extent to which the estimated current wheel circumference 14corresponds to the fallback wheel circumference 19. The characteristiccurve shows the extent to which the current wheel circumference 14 islearned and unlearned in relation to the constant fallback wheelcircumference 19. The current wheel circumference 14 is then calculatedin particular using the following equation:

Current wheel circumference=(coefficient from characteristic curve)*(wheel circumference estimated using single wheel-circumference values)+(1-coefficient from characteristic curve)*fallback wheel circumference

If the overall quality is 10, for example, a coefficient of 0.5 can beread off the characteristic curve in FIG. 4. In other words, half of thewheel circumference estimated on the basis of the singlewheel-circumference values 13 stored in the circular buffer 4 and halfof the fallback wheel circumference 19 go into the value for theestimated current wheel circumference 14.

The associated determined reference speed 10 at a relevant point in timemay also be stored in the circular buffer 4, the current wheelcircumference 14 being estimated exclusively on the basis of the singlewheel-circumference values 13 in the circular buffer 4 of which theassociated reference speeds 10 correspond to a speed range within whicha speed of the vehicle 50 lies at a current point in time. This allowsimproved estimation of the current wheel circumference 14, since onlysingle wheel-circumference values 13 of an associated speed range aretaken into consideration.

FIG. 5 shows a temporal progression of an estimated current wheelcircumference 14 for the purpose of clarifying the method, in particularwith respect to a learning and unlearning behavior of the current wheelcircumference 14. The time is shown on the x-axis 40 and the currentwheel circumference 14 estimated by means of the method and/or device(cf. FIG. 1) is shown on the y-axis 41. A minimum value 42, a maximumvalue 43 and the fallback wheel circumference 19 are drawn into thegraph.

The minimum value 42 is calculated on the basis of the wheelcircumference of the smallest tire provided and/or permitted, reduced bya margin of tolerance of 2.5%. The maximum value 43 is estimated basedon the wheel circumference of the largest tire provided and/or permittedfor the vehicle. A margin of tolerance of 1.5% is added to saidestimation. The fallback wheel circumference 19 is calculated on thebasis of a wheel circumference averaged from the tires provided for thevehicle 50, a margin of safety of 4% of the result also being added tothe result.

In the following, a temporal progression of the estimated current wheelcircumference 14 is described by way of example. At the beginning, thevehicle and the method are started. At this point, the estimated currentwheel circumference 14 corresponds to the fallback wheel circumference19, since the circular buffer has not yet been populated with asufficient number of estimated single wheel-circumference values. At apoint in time 44, the reference apparatus, for example a GNSS, providesfirst values for a reference speed, such that single wheel-circumferencevalues 13 can be estimated using the reference speed and the wheelrotational speed. The single wheel-circumference values 13 are lowerthan the estimated current wheel circumference 14. Since the circularbuffer is populated successively with additional values, its overallquality increases. As a result, the (averaged) wheel circumferenceestimated using the single wheel-circumference values 13 stored in thecircular buffer are weighted ever more strongly during estimation of thecurrent wheel circumference (cf. characteristic curve in FIG. 4). Untila point in time 45, the estimated current wheel circumference 14therefore decreases and gradually approaches the (averaged) singlewheel-circumference values 13.

At the point in time 45, the vehicle for example drives into a tunnel,and therefore the GNSS signal is no longer available, data pairsconsisting of reference speed and wheel rotational speed are deemedinvalid and therefore no more single wheel-circumference values 13 canbe provided. The current wheel circumference 14 therefore starts toapproach the fallback wheel circumference 19 again, since an overallquality of the circular buffer decreases with every time step (cf. FIG.4). The vehicle only leaves the tunnel at a point in time 46, at whichpoint the GNSS signal is available once more. The data pairs are thendeemed valid once again and single wheel-circumference values 13 areestimated once more. Consequently, the estimated current wheelcircumference 14 starts to approach the (averaged) singlewheel-circumference values 13 in the circular buffer once again, untilthe GNSS signal is interrupted again at a point in time 47. After thepoint in time 47, the estimated current wheel circumference 14 graduallyapproaches the fallback circumference 19 again.

This action of approaching the (averaged) single wheel-circumferencevalues 13 and fallback wheel circumference 19 corresponds to learningand unlearning of the (averaged) single wheel-circumference values 13.If the reference speed cannot be provided, the estimated current wheelcircumference 14 falls back to the fallback wheel circumference 19again. This way, the current wheel circumference 14 can always beestimated in a reliable manner.

FIG. 6 is a schematic signal flow diagram of an embodiment of the methodfor estimating a current wheel circumference of at least one wheelarranged on a vehicle. A GNSS as the reference apparatus 30 provides areference speed 10 of the vehicle. A wheel rotational speed 11 isprovided by a driving dynamics control system 52 of the vehicle, forexample an ESC. In method step 100, the reference speed 10 and the wheelrotational speed 11 are synchronized with one another in terms of theirtime base and/or the associated point in time, i.e., data pairsconsisting of a reference speed 10 and a wheel rotational speed 11 thatboth relate to the same point in time are created.

Subsequently, the data pairs are checked with regard to their validityin method step 101. The data pairs are deemed valid, for example, if asingle wheel-circumference value 13 estimated from the reference speed10 and wheel rotational speed 11 lies within a predetermined range(e.g., defined by the maximum value 43 and the minimum value 42 in FIG.5). For the data pairs that are deemed valid, the singlewheel-circumference value 13 calculated therefrom is stored in acircular buffer 4. The relevant associated reference speed 10 and therelevant associated wheel rotational speed 11 may also be stored in thecircular buffer.

In method step 102, the quality of the single wheel-circumference values13 stored in the circular buffer 4 is calculated. This is done, forexample, on the basis of the age and/or associated reference speed 10,for example using correspondingly formed characteristic curves (cf.,e.g., FIGS. 2 and 3). Furthermore, an overall quality of the circularbuffer is calculated based on the quality of each singlewheel-circumference value.

In method step 103, depending on whether there are corresponding singlewheel-circumference values 13 and/or whether said values have beendeemed valid, and depending on the calculated overall quality of thecircular buffer (cf. FIG. 4), the current wheel circumference 14 islearned 104 or unlearned 105 based on the (averaged) singlewheel-circumference values 13 (cf. also FIG. 5).

Finally, the estimated wheel circumference 14 is output as a wheelcircumference signal and can be used, for example, to estimate a currentspeed of the vehicle.

REFERENCE NUMBER LIST

1 Device

2 Input apparatus

3 Calculation apparatus

4 Circular buffer

5 Output apparatus

10 Reference speed

11 Wheel rotational speed

12 Data pair

13 Single wheel-circumference value

14 Current wheel circumference

15 Wheel circumference signal

16 Current speed

17 Quality

18 Overall quality

19 Fallback wheel circumference

20 x-axis

21 y-axis

22 Curve

24 x-axis

25 y-axis

26 Curve

27 x-axis

28 y-axis

30 Reference apparatus

40 x-axis

41 y-axis

42 Minimum value

43 Maximum value

44-47 Point in time

50 Vehicle

51 Wheel

52 Driving dynamics control system

53 Control system

100-105 Method steps

The invention has been described in the preceding using variousexemplary embodiments. Other variations to the disclosed embodiments canbe understood and effected by those skilled in the art in practicing theclaimed invention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. A single processor, module, or other unit or devicemay fulfil the functions of several items recited in the claims.

The mere fact that certain measures are recited in mutually differentdependent claims or embodiments does not indicate that a combination ofthese measured cannot be used to advantage. Any reference signs in theclaims should not be construed as limiting the scope.

1. A method for estimating a current wheel circumference of at least onewheel arranged on a vehicle, comprising: determining a reference speedof the vehicle at a point in time; sensing a wheel rotational speed ofthe at least one wheel at the point in time by a wheel rotational speedsensor; estimating a wheel-circumference value based on the determinedreference speed and the sensed wheel rotational speed for said point intime; storing at least the wheel-circumference value for said point intime in a circular buffer, which circular buffer uses FIFO logic;repeating the preceding for at least one other point in time so that aplurality of wheel-circumference values are stored in the circularbuffer; estimating a current wheel circumference based on the pluralityof wheel-circumference values stored in the circular buffer; andoutputting the estimated current wheel circumference for furtherprocessing.
 2. The method according to claim 1, wherein the currentwheel circumference is estimated based on a weighted mean value of theplurality of wheel-circumference values stored in the circular buffer.3. The method according to claim 1, wherein a validity of the determinedreference speed and sensed wheel rotational speed is checked, andwherein the wheel-circumference value only being estimated and storedfor a point in time if the determined reference speed and sensed wheelrotational speed are valid for said point in time.
 4. The methodaccording to claim 1, wherein a quality of at least one of the pluralityof wheel-circumference values stored in the circular buffer isdetermined.
 5. The method according to claim 4, wherein the quality isdetermined depending on an age of at least one of the plurality ofwheel-circumference values in the circular buffer.
 6. The methodaccording to claim 4, wherein the quality is determined depending on thedetermined reference speed associated with the respective singlewheel-circumference value.
 7. The method according to claim 1, whereinan overall quality of the circular buffer is determined, wherein thecurrent wheel circumference additionally being estimated on a basis ofthe ascertained overall quality of the circular buffer.
 8. The methodaccording to claim 7, wherein the current wheel circumference isestimated based on a characteristic curve, the characteristic curvedefining a weighting between a wheel circumference estimated on a basisof the plurality of wheel-circumference values stored in the circularbuffer and a fallback wheel circumference depending on the overallquality of the circular buffer.
 9. The method according to claim 1,wherein the determined reference speed at a respective point in time isalso stored in the circular buffer, wherein the current wheelcircumference being estimated exclusively on the basis of one or more ofthe plurality of wheel-circumference values in the circular buffer ofwhich the associated reference speeds correspond to a speed range withinwhich a speed of the vehicle lies at a current point in time.
 10. Adevice for estimating a current wheel circumference of at least onewheel arranged on a vehicle, said device comprising: an input apparatus;a calculation apparatus; a circular buffer; and an output apparatus;wherein the input apparatus is configured to receive a reference speedof the vehicle from a reference apparatus at least at one point in timeand to receive a wheel rotational speed of the at least one wheel from awheel rotational speed sensor at the at least one point in time; whereinthe calculation apparatus is configured to estimate awheel-circumference value based on the received reference speed and thereceived wheel rotational speed for the at least one point in time andto store at least the wheel-circumference value for said point in timein the circular buffer; wherein, in case a plurality ofwheel-circumference values are stored in the circular buffer for aplurality of points in time, the calculation apparatus is configured toestimate a current wheel circumference based on the plurality ofwheel-circumference values stored in the circular buffer; and whereinthe output apparatus is configured to output the estimated current wheelcircumference for further processing.
 11. The method according to claim5, wherein the quality is determined depending on the determinedreference speed associated with the respective wheel-circumferencevalue.
 12. The method according to claim 2, wherein a quality of theplurality of wheel-circumference values stored in the circular buffer isdetermined.
 13. The method according to claim 3, wherein a quality ofthe plurality of wheel-circumference values stored in the circularbuffer is determined.
 14. The method according to claim 2, wherein avalidity of the determined reference speed and sensed wheel rotationalspeed is checked, and wherein the wheel-circumference value only beingestimated and stored for a point in time if the determined referencespeed and the sensed wheel rotational speed are valid for said point intime.